Cyclobutadiene is said to be

Which of the following structures are aromatic in nature?

With respect to the compounds $\mathrm{I}-\mathrm{V}$ choose the correct statement(s).

Hydrogenation of cyclohexene and benzene take place as shown below. The resonance energy of benzene is $-36 {\mathrm{kcalmol}}^{-1}$

The relationship between $\mathrm{x}$ and $\mathrm{y}$ is

Among the following sets, the most stable ionic species are

Which compound amongst the following is not an aromatic compound?